388 Proceedings of the 



front of the vent, and in the specimens I have seen are con- 

 nected with one another by an unossified portion. Each ends 

 anteriorly in two processes projecting forwards. There are 

 six abdominal fin rays. From the pelvis on each side passes 

 outwards a ligament dividing into three parts, which are lost 

 in the aponeurotic sheath of the great lateral muscle. Bil- 

 harz pictures it in the Nilotic species. 



Modified Vertebrce. — The first vertebra is very small. Its 

 body is narrow, and the basi-occipital bone is prolonged under 

 it. The neurapophyses are separate little linear bones un- 

 connected with the body, and imbedded in fibrous membrane 

 immediately behind the occiput. The first vertebra has no 

 neural spine in this species, although in the Nilotic species 

 its neural spine is a distinct bone, as Dr Bilharz shows. Dr 

 Bilharz mentions another pair of small bones in connection 

 with the first vertebra ; but there is good reason to believe 

 that they are only part of the stapes bones, described below. 



The second, third, and fourth vertebrse are peculiarly modi- 

 fied, and almost inseparably united ; that is to say, in one 

 small specimen I succeeded in pulling the third and fourth 

 separate, but it is impossible to separate the second and third. 

 Dr Bilharz describes the second and third as one vertebra, 

 but they are certainly two. On the visceral surface, the com- 

 bined body of the three vertebrae exhibits distinctly the junc- 

 tion of the third and fourth by a deep toothed suture, and 

 indications of the still more thorough union of the second and 

 third. It presents in the middle line a large foramen, the 

 opening of a short canal which bifurcates in the substance of 

 the bone, and opens on each side under the posterior margin 

 of the transverse process of the second vertebra. The branchial 

 veins enter this Y-shaped canal, one at each side, and unite 

 in it to form the aorta. The transverse processes of these 

 vertebras arise from the neural arch. The neural arches of 

 the second and third vertebrse are fused in one continuous 

 lamina, without neural spine, and with a notch in front that 

 fits to a projection of the supra-occipital bone ; but at each side 

 a triangular space is left, the anterior part of which is occu- 

 pied by the little bones in connection with the first vertebra, 

 while from behind them issue the electric and other nerves. 



